1. Urogenital infection at screening Note: Urogenital infection includes urinary tract infection, Trichomonas (T.) vaginalis, Neisseria (N.) gonorrhoeae, Chlamydia (C.) trachomatis, Treponema (T.) pallidum, or vulvo-vaginal candidiasis. 2. Diagnosis of two or more outbreaks of N. gonorrhoeae, C. trachomatis, T. pallidum, T. vaginalis, or herpes simplex virus (herpes genitalis) within 6 months prior to screening 3. Positive for syphilis or HIV at screening 4. Current pregnancy or within 2 months of last pregnancy and/or currently breastfeeding**. Criteria will be assessed at screening and enrollment. 5. Vaginal or systemic antibiotic or antifungal therapy (other than MetroGel given as part of study procedures) within 21 days of screening or within 30 days of enrollment** 6. Use of disulfiram within past 2 weeks or other contraindication to use of MetroGel** 7. Any condition requiring regular periodic use of systemic antibiotics during participation in the trial 8. Active genital herpes lesion** (if not resolved by enrollment)** 9. Investigational drug use other than LACTIN-V within 30 days or 10 half-lives of the drug, whichever is longer, of enrollment visit** 10. Other planned participation in an investigational drug study while participating in this study** 11. Menopause defined as more than 12 consecutive months of amenorrhea without another known cause including pregnancy 12. IUD insertion or removal, pelvic surgery, cervical cryotherapy or cervical laser treatment within the last 2 months prior to screening 13. Use of vaginal ring (eg, NuvaRing) within 3 days of screening or during the course of the study** 14. Failure to complete 5 days of MetroGel with the last dose taken no later than 48 hours prior to randomization*** 15. Use of new long-acting hormonal treatments. Participant may be enrolled if stable (>3 months) on existing therapy as determined by the principal investigator** 16. Known allergy to any component of LACTIN-V/placebo or MetroGel or to nitroimidazole derivatives or latex (condoms) 17. Any social, medical, or psychiatric condition, including history of drug or alcohol abuse that in the opinion of the investigator would make it unlikely for the participant to comply with the study ** Note: Criteria will be assessed at screening and enrollment. ***Note: Criteria will be assessed at enrollment